1. Technical Field
The present invention relates to optical networks and, more particularly, to using legacy passive optical networks to carry orthogonal frequency division multiple access (OFDMA) signals and filtered legacy on-off keying (OOK) signals to limit interference between the OOK signals and the OFDMA signals.
2. Description of the Related Art
Passive optical networks (PONs) have been widely used in optical access networks to provide data signals. Legacy PONs use on-off keying (OOK) to transmit data along fiber optic cables. However, this existing infrastructure may also be used for mobile backhaul communications, providing access to the core network to mobile access points (e.g., cell towers) using orthogonal frequency division multiple access (OFDMA) signals. To reduce cost, it is desirable that remote-site optical receivers in these systems be colorless (i.e. wavelength-agnostic) and not need coherent detection or tunable optical filtering. However, a trade-off for these benefits is that interference between the OOK and OFDMA signals puts a limit on how far the signals can be transmitted as well as on the split ratio.